1. Field of Invention
Aspects of the present invention relate to machine vision methods for locating features on an object using varied illumination.
2. Description of Background Information
A vision tool exists that measures the area and location of solder paste printed on circuit boards for the purpose of inspecting the prints made for solder paste screen printing machines. The method used compares a pre-print image of the circuit board at a given inspection site with a post-print image of the circuit board at the given inspection site to determine which pixels in the post-print image are solder paste. An inspection site can be, for example, an entire circuit board or a sub-part of a circuit board depending upon a field of view of the optics used. The identified pixels are then grouped into regions and measured by a xe2x80x9cblobxe2x80x9d tool.
The main limitation of the above method is that two images of each inspection site of each circuit board must be acquiredxe2x80x94a before printing image and an after printing image. Moving the camera from inspection site to inspection site takes time and reduces the throughput of the method.
In an embodiment of the invention, a method is provided for locating features of an object using varied lighting. An object is illuminated and a first digital image of the object is acquired. An illumination of the object is varied and a second digital image of the object is acquired while a camera and the object are in a same position as were the camera and the object during the acquisition of the first digital image. One of the first and the second digital images is subtracted from another of the first and the second digital images to produce a difference image. At least one feature of the object is located based on the difference image.